Chemical Defoliation Research Articles

The systemic herbicide glyphosate affects the sporulation dynamics of Rhizophagus species more severely than mechanical defoliation or the contact herbicide diquat.

Arbuscular mycorrhizal fungi (AMF) are totally dependent on a suitable host plant for their carbon resources. Here, we investigated under in vitro conditions, the impact of defoliation practices, i.e., mechanical defoliation or chemical defoliation with a contact herbicide (Reglone®, containing the active ingredient diquat) or systemic herbicide (RoundUp®, containing the active ingredient glyphosate),on the dynamics of spore production of Rhizophagus irregularis and Rhizophagus intraradices associated with Solanum tuberosum and/or Medicago truncatula. Glyphosate affected the spore production rate more rapidly and severely than diquat or mechanical defoliation. We hypothesize that this effect was related to disruption of the C metabolism in the whole plant combined with a possible direct effect of glyphosate on the fungus within the roots and/or perhaps in soil via the release of this active ingredient from decaying roots. No glyphosate could be detected in the roots due to technical constraints, while its release from the roots in the medium corresponded to 0.11% of the active ingredient applied to the leaves. The three defoliation practices strongly affected root colonization, compared to the non-defoliated plants. However, the amount of glyphosate released into the medium did not affect spore germination and germ tube growth. These results suggest that the effects of defoliation on the dynamics of spore production are mainly indirect via an impact on the plant, and that the effect is faster and more marked with the glyphosate-formulation, possibly via a direct effect on the fungus in the roots and more unlikely on spore germination.

Influence of time of pruning, bahar treatment followed by chemical defoliation on Jasminum sambac (L.)

Influence of time of pruning, bahar treatment followed by chemical defoliation on Jasminum sambac (L.)

Dissecting the biochemical and hormonal changes of thidiazuron on defoliation of cotton CO17 (Gossypium hirsutum) to enhance mechanical harvest efficiency

Using chemical defoliants to remove cotton leaves represents a groundbreaking shift in cotton cultivation. The mechanization of cotton harvest is increasing, but a substantial amount of foliage that remains on the plant even at maturity is the major barrier for mechanical harvest. Properly completing mechanical and manual harvests requires artificial leaf detachment through defoliants. Still there is no proper defoliant concentration, application times and mechanism of action available. Therefore, the present study aimed to find an effective defoliant and application time to enhance mechanical harvest efficiency, along with a clear description of the mechanism of actions in cotton CO17 (Gossypium hirsutum). The field experiment was conducted during the year 2019-20 and used five concentrations of Thidiazuron defoliant (100, 150, 200, 250 and 300ppm) and Ethephon@0.5% (T2) in cotton variety CO17 to study the physiological, biochemical and hormonal responses at 120, 127 and 134 days after sowing. As a result, the concentrations of plant growth hormones, indole-3 acetic acid (4.9 fold), zeatin (32.7%) and gibberellic acid (7 fold) reduced. In contrast, abscisic acid (48.6%), jasmonic acid (34.9%), salicylic acid (2.15 fold) increased in the T7- Thidiazuron + Diuron (300 ppm) treatment followed by T5-Thidiazuron + Diuron (200 ppm). Additionally, the antioxidant enzymes ascorbate peroxidase, peroxidase, catalase, superoxide dismutase, cellulase in leaves, petiole and bolls were decreased due to defoliant T5- Thidiazuron + Diuron (200 ppm) followed by T7-Thidiazuron + Diuron (300 ppm), indicating that the hormone concentration, antioxidative and hydrolytic enzymes are ruled out and forces the defoliation process.

Physiological adaptations of the Japanese plum tree for agricultural productivity: A promising crop for high altitude tropics

The Japanese plum tree is of great importance in the productive development of Colombian fruit growers due to its nutritional contribution to human health, its great adaptability in the tropical highlands, and its good yields. This review presents the current investigative state of physiology of this plant and its management in tropical highlands, including aspects such as its ecophysiology, forced production, gas exchange, flowering, pollination, and fruit development. In Colombia, Japanese plum production systems are adapted between 1,670 and 2,900 m a.s.l., average solar brightness of 1,400 h per year, 12 h photoperiods, temperatures between 14 and 20°C during the day and 6 and 8°C during the night, and rainfall between 700 and 1,600 mm per year. Under these conditions, management can be implemented to produce cyclical crops of the Japanese plum. This management consists of the selection of varieties with low chilling requirement, chemical defoliation, proper fertilization, fruit and green pruning, and the application of chemical substances that promote the breaking of flower buds. Flowering and pollination require a high specificity so that they do not present incompatibility. The growth and development of the fruit requires 1,538 degree days until harvest. This review indicates the great adaptability, management, and production of Japanese plum in the Colombian high tropics.

Application of defoliants alters leaf growth and gas exchange parameters for cotton defoliation

The goal of the current study was to determine how different chemical defoliants and application timing affected defoliation in cotton variety CO 17. The studies were conducted using a split-plot design with three applications at three different times as the main plot and seven defoliants as the subplot. Thidiazuron + Diuron (0.03%) defoliant reduced the gas exchange parameters, photosynthetic rate, transpiration rate and stomatal conductance by reducing plant growth parameters, leaf area, leaf area index, specific leaf weight which significantly increased the defoliation percentage. The negative correlation of cotton growth and gas exchange parameters with defoliation percentage was observed in correlation studies. In conclusion, Thidiazuron + Diuron (0.03%) defoliant was found to be superior in action for improving leaf defoliation and its associated parameters. And also it may be a cost-effective cotton defoliant for aiding the mechanical picking of cotton bolls.

Comparative Physiological and Transcriptomic Mechanisms of Defoliation in Cotton in Response to Thidiazuron versus Ethephon.

Thidiazuron (TDZ) is a widely used chemical defoliant in cotton and can stimulate the production of ethylene in leaves, which is believed to be the key factor in inducing leaf abscission. Ethephon (Eth) can also stimulate ethylene production in leaves, but it is less effective in promoting leaf shedding. In this study, the enzyme-linked immunosorbent assays (ELISA) and RNA-seq were used to determine specific changes at hormonal levels as well as transcriptomic mechanisms induced by TDZ compared with Eth. The TDZ significantly reduced the levels of auxin and cytokinin in cotton leaves, but no considerable changes were observed for Eth. In addition, TDZ specifically increased the levels of brassinosteroids and jasmonic acid in the leaves. A total of 13 764 differentially expressed genes that specifically responded to TDZ were identified by RNA-seq. The analysis of KEGG functional categories suggested that the synthesis, metabolism, and signal transduction of auxin, cytokinin, and brassinosteroid were all involved in the TDZ-induced abscission of cotton leaves. Eight auxin transport genes (GhPIN1-c_D, GhPIN3_D, GhPIN8_A, GhABCB19-b_A, GhABCB19-b_D, GhABCB2-b_D, GhLAX6_A, and GhLAX7_D) specifically responded to TDZ. The pro35S::GhPIN3a::YFP transgenic plants showed lower defoliation than the wild type treated with TDZ, and YFP fluorescence in leaves was almost extinguished after treatment with TDZ rather than Eth. This provides direct evidence that GhPIN3a is involved in the leaf abscission induced by TDZ. We found that 959 transcription factors (TFs) specifically responded to TDZ, and a co-expression network analysis (WGCNA) showed five hub TFs (GhNAC72, GhWRKY51, GhWRKY70, GhWRKY50, and GhHSF24) during chemical defoliation with TDZ. Our work sheds light on the molecular basis of TDZ-induced leaf abscission in cotton.

Chemical Defoliation in the Vine Nursery

The trial was carried out in the period 2017-2020 in a vine nursery located on slightly leached chernozem. The objective of the study was to investigate the opportunities of applying the contact foliar herbicides Basta 15 SL (150 g/l glufosinate-ammonium) and Diqua 20 SL (200 g/l diquat) as defoliants, immediately before removing the vines from the nursery (the second half of October). Their effect on the above-ground vegetative mass of the grafted rooted vines of the varieties Muscat Plevenski, Bolgar, Naslada and Storgozia was established. The herbicides were applied in different doses, once and twice at the end of the growing season with work solution of 50 l/da. The strongest defoliating effect in all varieties was reported after treatment with Diqua 20 SL at a dose of 0.6 l/da and the combination of Basta + Diqua (0.3 + 0.33 l/da) with two applications, but in case it was not possible the second treatment to be performed, a satisfactory result might be achieved with a single application of the herbicides no later than 15 days before removing the vines from the nursery. To prove the vines’ capacity for development during the next growing season, the status of their buds after the treatment with the tested herbicides was determined. No negative vines’ response caused by this type of defoliation was found.

How to Improve the Production and Quality of Chirimoya (Annona cherimola Mill.) in the Tropical Andes

The production of chirimoya (Annona cherimola Mill) is seasonal; therefore, the fruit's prices and availability are compromised. This research aimed to develop technologies to improve the production and competitiveness of off-season chirimoya fruit production. This research was conducted in the subtropical valley of Tumbaco, Pichincha province, Ecuador. Chemical defoliants (zinc sulfate, hydrogenated cyanamide, and copper chelate) and a sprouting inducer (hydrogenated cyanamide) were evaluated to standardize and increase defoliation improve sprouting, and consequently bring the harvest season forward. The study was conducted on eight-year-old trees of San José de Minas and MAG-Tumbaco genotypes. The assessed variables were defoliation, sprouting, elapsed flowering time, and harvest period. The fruit harvest was shortened by 18.4 days by applying the defoliants and sprout inducer. For the San José de Minas genotype, the best response for defoliation (99%) was copper chelate at 1%, compared to the control with 58.9% defoliation at 35 days after its application. In the MAG-Tumbaco genotype, the best defoliation results were also obtained with cooper chelate at 1% (99.7% defoliation), while the control achieved 95.5% for 35 days after its application. In the latter genotype, defoliants significantly outperformed the control in terms of sprouting at 21 and 28 days after application; as a result, harvest was advanced by 22.6 days. These treatments should be tested in other climate zones to establish them as cultural practices to increase off-season fruit production, benefiting farmers and industry.

Type of Stress Induces Differential Responses in Acer rubrum (Red Maple), but Induced Responses Have No Effect on Herbivorous Pests

Plants thrive in dynamic environments requiring adaptive strategies in response to environmental stressors. Furthermore, insect herbivores may be attracted or deterred by the expression of these traits. This study examines growth, physiological, and phytochemical adaptations of maple trees in response to stressors and how these stressors effect herbivore feeding behavior within an agricultural production system. Agricultural systems are unique because plants experience environmental stressors unique to production such as herbicide sprays and girdling. Using four environmental stressors commonly observed in agricultural production (control, mechanical defoliation, chemical defoliation, and girdling), applied to two cultivars of red maple (Acer rubrum, ‘Brandywine’ and ‘Franksred’), this study analyzed differentiation of expressed traits in a production system. Responses varied depending on cultivar and stress treatment but had no effect on insect herbivore behavior. Understanding the ecological interactions within these systems will provide information for better plant production and pest management recommendations.

Construction of Thermoresponsive Microcapsules for the Controlled Release of Thidiazuron to Improve Defoliation Effects

The successful defoliation of cotton leaves by using chemical defoliants is extremely important for the mechanical harvest of cotton, which can greatly reduce the impurity content of cotton. Howeve...

Impact of Chemical Defoliants on Chlorophyll Fluorescence, Biochemical Parameters, Yield and Fiber Quality of High Density Cotton

Background: The Cotton growing farmers in India are facing major problem at the time of harvest due to labor shortages, asynchronized boll opening, leaf trash in the cotton, which is reducing the boll picking efficiency and fiber quality. Presently, the Indian cotton industry is moving towards mechanical harvesting by cotton harvester. Defoliation or leaf abscission is induced in cotton as a natural physiological process which usually is inadequate for a complete mechanical harvest of cotton. Defoliation before harvest is often induced by managing the plants so that senescence, abscission (separation) layer development and leaf drop are encouraged. Chemical defoliants induce leaf abscission, hasten mature boll dehiscence and inhibit re­ growth. Selection of appropriate defoliants is one of the critical decisions in cotton production. Their use can result in increased manual as well as machine harvest efficiency, reducing boll rot and the trash in seed cotton. The physiological basis of defoliation in cotton is essential to understand the role of appropriate defoliant with time of application. Hence, the objective of the study was to evaluate the defoliation efficiency, boll opening percentage and to know the physiological basis of defoliation in response to different defoliants and time of application in high density Cotton cultivation which eases the mechanical harvesting.Methods: In this field investigation during 2018 - 2019 at Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore was carried with seven different defoliants and three different time of defoliants application were fixed based on crop maturity and duration of the crop. In this study, high density cotton variety CO 17 was used as experimental material. A series of lab and field analysis were determined on defoliation process, physiological attributes, boll opening percentage and seed yield and quality. The collected data were subjected to statistical analysis.Result: Our investigation exploring the effect of different defoliants on physiological, biochemical, yield and quality parameters of high density Cotton. Among the different defoliants and time of applications, two defoliants and two times of applications works better in terms of better defoliation, boll opening rate, physiology, yield and quality. The physiological and biochemical effects of defoliants on defoliation process were discussed. The present work will be useful for mechanized picking with these effective defoliants without loss of yield and quality loss in cotton.

Migration of Oil Bodies in Embryo Cells during Acquisition of Desiccation Tolerance in Chemically Defoliated Corn (Zea mays L.) Seed Production Fields

Chemical defoliation of seed corn production fields accelerates seed maturation and desiccation and expedites seed harvest. Early seed harvest is important to minimize the risk of frost damage while in the field. This newly adopted seed production practice also allows seed companies to plan harvest and manage dryer space more efficiently. However, premature defoliation may interfere with the migration of oil bodies within embryo cells during desiccation and affect seed germination and vigor. The objective of this study was to investigate the effect of chemical defoliation on the migration patterns of oil bodies within embryo cells during desiccation. Chemically defoliated and non-defoliated plants from five commercial hybrid seed corn fields were sampled in 2014 and 2015. Whole ears with husks were harvested before and after defoliant application at 600 g H2O kg−1 fresh weight (fw), and weekly thereafter until seed reached approximately 300–350 g H2O kg−1 fw. Ten embryos extracted from center-row seeds were fixed to stop metabolic processes, then sliced, processed, and photographed using scanning transmission electron microscopy. The oil bodies within embryo cells followed normal migration patterns according to seed moisture content, regardless of defoliation treatment. Seed germination and vigor were verified and were not significantly affected by defoliation. Chemical defoliation is a viable production practice to accelerate seed corn desiccation and to manage harvest and seed dryer availability more efficiently without negatively affecting seed germination and vigor.

Evaluation of Cotton (Gossypium hirsutum L.) Leaf Abscission Sensitivity Triggered by Thidiazuron through Membership Function Value.

Chemical defoliation is an essential agricultural practice in cotton production for mechanic harvesting. Thidiazuron (TDZ) is the active ingredient of the chemical defoliant used on cotton. So far, few studies havefocused on the method of identifying the sensitivity of cotton cultivars to TDZ. Therefore, a greenhouse soil culture experiment was performed by using two widely cultivatedupland cotton cultivars CRI 49 and CRI 12 treated with seven different concentrations (0, 100, 200, 300, 400, 500, and 1000 mg L−1) of TDZ at the seedling stage to establish a screening system. Principal component analysis and the membership function value (MFV) method was used to analyze the physiological and phenotypic characters, including abscission rate, amino acids content, net photosynthetic rate (Pn), etc. Finally, we developed a mathematical evaluation model, selected 100 mg L−1 TDZ as the optimal concentration and identified reliable characters net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) to evaluate cotton leaf abscission sensitivity. These results also confirmed that CRI 12 was more sensitive to TDZ than CRI 49. This is the first time using a mathematical evaluation method to evaluate the cotton leaf abscission sensitivity triggered by TDZ at the seedling stage and the results were also confirmed in the field experiment. Furthermore, it will be valuable that MFV method is applied to stress sensitivity evaluation in other crop species under stress environment.

Involvement of Hydrogen Peroxide in Cotton Leaf Abscission Induced by Thidiazuron

Thidiazuron (TDZ) has been extensively applied as chemical defoliant in cotton production, but the physiological mechanisms for its defoliating activity are poorly understood. Hydrogen peroxide (H2O2) is regarded as an endogenous regulator of abscission. In the current study, we found that H2O2 was involved in cotton leaf abscission induced by TDZ. TDZ induced water loss, cell death, and oxidative injury in cotton leaf, leading to significant leaf abscission. TDZ treatment induced a significant increase in H2O2 production in the leaf, petiole and abscission zone. Treatment with DPI, a respiratory burst oxidase homologue inhibitor, significantly inhibited TDZ-induced H2O2 generation, coinciding with a remarkable decrease in leaf abscission. TDZ treatment stimulated the expression of RbohA in the petiole and pulvinus. These results suggest that H2O2 might play an important role in cotton leaf abscission induced by TDZ.

Effect of Different Defoliants and Time of Application on Defoliation Percentage and Boll Opening Percentage in High Density Cotton (Gossypium hirsutum L.)

Aims: To evaluate the time and type of chemical defoliants to improve the mechanical and manual picking of high density cotton CO 17 in terms of higher defoliation and increase boll opening percentage.
 Study Design: The study was performed in split plot design with seven treatments and four replications.
 Place and Duration of Study: This field study was carried out in Department of Crop Physiology TNAU, Coimbatore during September 2019 to January 2020.
 Methodology: Three time of defoliants application (120 Days After Sowing (DAS), 127 DAS and 134 DAS) for main plot and seven treatment levels of Control, 2, 4 D (0.5%), Ethephon (0.5%), Ethephon (0.5%) + TIBA (450 ppm), Sodium chlorate (0.9%), 6-BAP (0.1%), Thidiazuron + Diuron (0.03%) for sub plot.
 Results: Defoliation percentage was significantly enhanced from 4 days after defoliants spray. Boll opening percentage also increased with defoliants spray when compared to control plants. Although a significant effect was observed on SPAD value, NDVI value and seed cotton yield.
 Conclusion: From this study, application of Thidiazuron + Diuron (0.03%) and Sodium chlorate (0.9%) had significantly positive effect in per cent defoliation and boll opening percentage and it will work better in young cotton plants compare to mature one.

Relationship among chemical defoliation, vegetative reproductive parameters and entomosporium leaf spot (Entomosporium mespili) of pear in southern Brazil

Relationship among chemical defoliation, vegetative reproductive parameters and entomosporium leaf spot (<i>Entomosporium mespili</i>) of pear in southern Brazil

Winter cold deficit in low subtropical climate region and blackberry varieties phenology

In the western region of Paraná, the subtropical climate prevails, with little accumulation of hours of cold in the winter, making the fruit species not go into complete dormancy. Given the above, the objective of this study was to evaluate the effect of chemical defoliant on blackberry varieties, aiming at their complete defoliation and induction of numbness. The work was conducted at Unioeste, Marechal Cândido Rondon Campus, in a four-year-old orchard of plants, spaced 3 x 0.5 m, simple spreader with two wire strands at a height of 120 cm from the ground, and 20 plants per grow crops. The experimental design used was randomized blocks, where two treatments related to the application of defoliant (with and without) on 7 cvs were evaluated blackberry, containing three replicates and three plants in each cultivar. Was used as a defoliant lime sulfur applied in August pruning then held 25 days after application. Regarding fruit quality, Caigangue and Tupy varieties showed the highest SS/AT ratio, indicating the best flavor of their fruits for fresh consumption. The cultivars Brazos and Guarani showed lower SS/AT ratio, indicating more acidic fruits. Higher levels of ascorbic acid were found in fruits of cvs. Guarani and Cherokee. The application of defoliant reduced the total number of blackberry fruits of the cultivars Comanche and Guarani. The use of defoliant did not interfere in the physicochemical characteristics of the blackberry fruits of the evaluated cultivars.

Chemical Defoliant Promotes Leaf Abscission by Altering ROS Metabolism and Photosynthetic Efficiency in Gossypium hirsutum.

Chemical defoliation is an important part of cotton mechanical harvesting, which can effectively reduce the impurity content. Thidiazuron (TDZ) is the most used chemical defoliant on cotton. To better clarify the mechanism of TDZ promoting cotton leaf abscission, a greenhouse experiment was conducted on two cotton cultivars (CRI 12 and CRI 49) by using 100 mg L−1 TDZ at the eight-true-leaf stage. Results showed that TDZ significantly promoted the formation of leaf abscission zone and leaf abscission. Although the antioxidant enzyme activities were improved, the reactive oxygen species and malondialdehyde (MDA) contents of TDZ increased significantly compared with CK (water). The photosynthesis system was destroyed as net photosynthesis (Pn), transpiration rate (Tr), and stomatal conductance (Gs) decreased dramatically by TDZ. Furthermore, comparative RNA-seq analysis of the leaves showed that all of the photosynthetic related genes were downregulated and the oxidation-reduction process participated in leaf shedding caused by TDZ. Consequently, a hypothesis involving possible cross-talk between ROS metabolism and photosynthesis jointly regulating cotton leaf abscission is proposed. Our findings not only provide important insights into leaf shedding-associated changes induced by TDZ in cotton, but also highlight the possibility that the ROS and photosynthesis may play a critical role in the organ shedding process in other crops.

Effect of chemical defoliation on boll opening and yield of cotton

A field experiment was carried out for two consecutive years kharif, 2014 and 2015 at instructional farm of Rajasthan College of Agriculture, Udaipur, Rajasthan to study the effect of different defoliants at different doses on cotton and residual effect on succeeding greengram crop. The experiment laid out on sandy clay loam soil by adopting randomized block design which included four replication and seven treatments viz. Untreated check, Diquat dibromide 24.5 SL W/V 551.25 g a.i. ha-1 (2250 ml/ha), Diquat dibromide 24.5 SL W/V 735 g a.i. ha-1 (3000 ml/ha), Diquat dibromide 24.5 SL W/V 918.75 g a.i. ha-1 (3750 ml/ha), Diquat dibromide 24.5 SL W/V 1102.5 g a.i. ha-1 (4500 ml/ha), Paraquat dichloride 24 SL 300 g a.i. ha-1, (1250 ml/ha) Mepiquat chloride 5%AS 62.5 g a.i. ha-1 (1250 ml/ha. Variety Super Mallika was taken during kharif season as test crop. Result revealed that application of Diquat dibromide 24.5 SL W/V at 1105 g a.i. ha-1 at 60-70 per cent boll opening stage of cotton crop appears to be promising treatment as it gave significantly higher defoliation, boll opening and seed cotton yield with no phytotoxic effects on cotton bolls and residual crop.

Innumerable squamous cell carcinomas in a Vietnam War veteran exposed to chemical defoliants

Objective. We present a successful multidisciplinary treatment approach used for a patient with rapidly developing, high-volume, and high-risk squamous cell carcinomas (SCCs), addressing short-term treatment, long-term maintenance, and appropriate preventative strategies in a difficult patient population. Case report. An immunocompetent, 84-year-old, Caucasian man with at least 30 SCCs of the scalp, head, neck, and upper extremities, including a 4-cm SCC on the vertex of the scalp infiltrating to the periosteum, presented to a cutaneous oncology clinic. Initial physical examination revealed nearly confluent, erythematous, hyperkeratotic, crusted papules and plaques on the head, neck, back, arms, and dorsal hands, all of which were clinically obvious SCC. Nonlesional skin displayed widespread epidermal dysplasia. The patient was seen by the clinic's medical oncology and dermatology teams in coordinated dual visits. The invasive scalp lesion was treated by Mohs surgery and radiation, and the large SCC and field cancerization were successfully treated with a combination of topical and intralesional 5-fluorouracil with pulsed oral capecitabine, which resulted in a significant reduction in SCC disease burden. Conclusion. Management of patients with overwhelming numbers of SCCs is extremely challenging. Combination topical and/or intralesional 5-fluorouracil and oral capecitabine may be considered as part of the management approach when mechanical destruction and surgery alone are not feasible. Multidisciplinary care coordinated between the surgeon, dermatologic oncologist, medical oncologist, and radiation oncologist is essential for providing comprehensive treatment and deploying preventative strategies in this population at high risk for metastatic SCC formation.